Molecular Functions of Set in Chromosome Stability and Aging PROJECT SUMMARY: Increasing evidence supports that aneuploidy, wrong number of chromosomes in cells, significantly contributes to aging. Aneuploidy usually arises from chromosome missegregation during cell division. Therefore, to understand the mechanisms that govern chromosome segregation is critical for dissecting the underlying causes of aneuploidy and its associated aging. The objectives of this project are to elucidate a critical mechanism that control chromosome segregation and also how de-regulation of the mechanism contributes to aging and aging-related disease, such as cancer. Sister-chromatid cohesion, mediated by the cohesin complex (Smc1/Smc3/Scc1/SA1,2), is one of the factors that are essential for chromosome stability. It is established during S phase and resolved during mitosis. At early mitosis, the bulk of cohesin on chromosome arms is released and centromeric cohesin is protected by the conserved protein family Shugosin (Sgo1) until anaphase onset. We found that early establishment of the Sgo1-cohesin interaction and later disruption of this interaction during mitosis are critical for proper chromosome segregation. However, the mechanism that disrupts the Sgo1-cohesin interaction is not understood at all. We recently identified Set/I2PP2A as a cellular inhibitor to the essential Sgo1-cohesion interaction. Interestingly, Set is highly expressed in a wide range of cancers and is believed to be an oncogenic protein. Based on these, we hypothesize that Set promotes chromosome segregation through physically inhibiting Sgo1-cohesin interaction at metaphase to anaphase transition, and that overexpression of Set induces chromosome missegregation leading to aneuploidy via ectopically weakening Sgo1-cohesin interaction, which promotes aging and tumorigenesis. Three specific aims will be fulfilled to test this hypothesis: we will determine (1) how Set de-protects centromeric cohesion at metaphase to anaphase transition, (2) how overexpression of Set results in aneuploidy, and (3) role of Set in aging. With the expected results, we will decipher the molecular mechanisms that inactivate centromeric cohesion, which is critical for chromosome segregation at metaphase to anaphase transition, and also reveal the roles of Set in aging and aging-related diseases, such as cancer. This project is relevant to public health because de-regulation of sister cohesion leads to chromosome missegregation and aneuploidy, which is known to drive aging and various types of diseases. The outcome of this proposed work is expected to provide the molecular mechanisms that properly regulate sister-chromatid cohesion, which prevents chromosome missegregation and formation of aneuploidy.